I have my new Stew Mac OOO bolt on neck guitar kit, and am preparing for my first actual construction steps. A question I have is with the bolt on neck, what is recommended for side to side clearance in the joint to the body, and what about using shims to fill in any excess space?

I inspected the parts in my kit closely, and when I slipped the neck into the neck block, I was surprised that there was so much play in the joint. I measured both the neck tenon and the neck block mortise, and there is .057" side to side clearance between them, which seems like a lot to me.

I emailed Stew Mac, and they replied back that "Some clearance on the sides of the tenon is necessary so that there can be side to side movement of the neck", and "Shims can be used to align the neck with the center of the body". The Stew Mac "Assembly Instructions" book states that "A bolt-on neck doesn’t require a shim, and is not intended to fit tightly like the dovetail". On the Stew Mac DVD, Todd Sams says with the bolt on neck, you "Make no shims". The contradiction in the reply versus the instructions puzzles me more than addressing my concern.

I would appreciate hearing some experiences with this from people that have built the Stew Mac bolt on neck kit. Thanks!

I have attached a sketch I made that shows the measurements I took.

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I have no answer, I'm afraid, but now you've got me wondering too. I'm doing a bolt-on neck for my Regal mandolin rebuild, and I've made the tenon a no-slop easy sliding fit into the mortise -- or whatever the proper terms are for a joint like this. That seemed to me to be the way to go, but that was just my guess.

Given the amount of pressure on the face surfaces when the instrument is strung up, I can't imagine the neck will go anywhere even if there is side clearance. On the other hand, I see no reason to have side clearance, except to the extent that it permits adjustment of neck alignment when installing the neck. If 'twere me, once alignment was established I'd shim it to a no-slop but easy slide fit. Of course, I seem to guess wrong about this stuff a lot.

With you, I await an authoritative answer.

_________________Everybody is ignorant, only on different subjects. -- Will RogersThere are lots of people who mistake their imagination for their memory. - Josh BillingsAnything is possible if you don't know what you are talking about.

I have completed a few bolt-on necks and am not an authority, but can offer a couple of observations. The bolt performs the function of the traditional dovetail of drawing the cheeks of the heel tight against the sides. The fit of the cheeks determines the neck alignment to the centerline and the angle of the fingerboard to the top. Those are the critical fitting issues. The tenon should be snug and the bolt should be tightened properly each trial fitting. I would strongly encourage you to watch the neck fitting videos from Blues Creek on youtube. Although those are for traditional dovetail joints, the principles are the same.

The bolts are pulling the the cheeks of the neck heel down on the rims. That is the joint. There is some side to side slop in the joint and a gap is left on the bottom of the tenon. A glued mortise and tenon joint would need a tight fit. I do not use shims on a mortise and tenon bolt on. Stew Macs response of shims can be used and the instructions "A bolt-on neck doesn’t require a shim" is not contradictory as both statements are true.

When I rout out the M&T for guitars the tenon is slightly larger than the mortise and I sand it down so it slides in with slight resistance. To me .057" is too much play. The some of my shim stock is .027" thick so that would be 2 pieces thick. If it was mine I glue on some shims and sand back if necessary. My 2 cents.

A joint should be snug. You shouldn't have to force it but there should not be slop. Yes you can shim the joint as this is a true blot on joint. I am not a fan of the bolt on system Stew mac uses. Also Stew Mac was sold out to a parent company.

I just went back to Stew Mac with another email asking for clarification on the bolt on neck joint mortise and tenon dimensions, and detailed assembly instructions. I will share the response when I receive it.

I received a reply back from Stew Mac on the clarification I asked for. It is as follows:

"The dimensions of your neck tenon and neck block match our specs although the tenon of the neck I measured was slightly shorter (by about .090") than what you indicated in your drawing. That could be the result of how it was measured. It's not a significant difference since the sides will be in between the neck heel and block. The width of the block compared to the tenon was the same as your drawing. That allows side to side play to line up the neck laterally."

"I mentioned that shims can be used since I have used them before in bolt-on construction. I discussed this with Todd and confirmed that a shim is not necessary for the best result. The neck angle and lateral position is determined by the contact of the cheeks of the heel with the sides. The bolts provide the proper strength and added shims would be overkill. I apologize for the conflicting info."

Given this information from Stew Mac, I will plan on fitting the neck and leave the fingerboard extension initially unglued. With the neck angle then set, I could size some shims to get them to fit in the joint while keeping the desired neck angle. I would ultimately like for the tenon to be snug as John pointed out.

Stewmac response was always my understanding of their joint. I think the tenon is only there to provide enough wood for the bolt to screw into. It is not really a mortise and tenon joint as it is not glued so there is no joint between the mortise and the tenon. The only joint is between the cheeks and the sides held by the bolts.

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